How to merge cells? remove borders of cells and make it one large cell?

Sometimes you have to fill large text into a single cell, but you don’t want to change the column width. An example is table heading.  To do that Select cell’s you wish to Merge from the home tab menu. Corner of the Merge command press drop down menu will appear. From here
Merge & Center: Merges the selected cells into one cell and text will place into the centre of the cell
Merge Across: Merges the selected cells into larger cells while keeping each row separate
Merge Cells: Merges the selected cells into one cell, but does not centre the text

Unmerge Cells: Unmerges selected cells 

How to fill large text in to a cell? Change cells size to fit large content? How to Increase the cell’s row height ?

Whenever you have a large text needs to place into a single cell, for that we have two options one is merge the cells another one wraps the text. 

Select cell’s you wish to wrap the text from the home tab menu. Select the same wrap the text menu to unwrap the text.

How to unhide columns and rows in excel

When we hide the column or row the hidden column or row become a green line. if we want to unhide column or row
First, we need to select both sides of rows or columns of the hidden columns or rows

Right click the mouse and select the unhide from the menu. The hidden columns or rows reappear again